Powershell Shell Detection

# PowerShell detection
if ($env:PSModulePath) {
    Write-Host "Running in PowerShell"
    # PSModulePath contains 3+ paths separated by semicolons
    $env:PSModulePath -split ';'
}

# Check PowerShell version
$PSVersionTable.PSVersion
# Output: 7.5.4 (PowerShell 7) or 5.1.x (Windows PowerShell)

PowerShell-Specific Variables:

# These only exist in PowerShell
$PSVersionTable    # Version info
$PSScriptRoot      # Script directory
$PSCommandPath     # Script full path
$IsWindows         # Platform detection (PS 7+)
$IsLinux           # Platform detection (PS 7+)
$IsMacOS           # Platform detection (PS 7+)

Shell Type Detection in Scripts

function Get-ShellType {
    if ($PSVersionTable) {
        return "PowerShell $($PSVersionTable.PSVersion)"
    }
    elseif ($env:PSModulePath -and ($env:PSModulePath -split ';').Count -ge 3) {
        return "PowerShell (detected via PSModulePath)"
    }
    else {
        return "Not PowerShell"
    }
}

Get-ShellType

Git Bash / MSYS2 Detection

Primary Indicators

MSYSTEM Environment Variable (Most Reliable):

# Bash detection in Git Bash/MSYS2
if [ -n "$MSYSTEM" ]; then
    echo "Running in Git Bash/MSYS2: $MSYSTEM"
fi

# MSYSTEM values:
# MINGW64 - Native Windows 64-bit environment
# MINGW32 - Native Windows 32-bit environment
# MSYS    - POSIX-compliant build environment

Secondary Detection Methods:

# Using OSTYPE (Bash-specific)
case "$OSTYPE" in
    msys*)   echo "MSYS/Git Bash" ;;
    cygwin*) echo "Cygwin" ;;
    linux*)  echo "Linux" ;;
    darwin*) echo "macOS" ;;
esac

# Using uname (Most portable)
case "$(uname -s)" in
    MINGW64*) echo "Git Bash 64-bit" ;;
    MINGW32*) echo "Git Bash 32-bit" ;;
    MSYS*)    echo "MSYS" ;;
    CYGWIN*)  echo "Cygwin" ;;
    Linux*)   echo "Linux" ;;
    Darwin*)  echo "macOS" ;;
esac

Cross-Shell Compatibility on Windows

Critical Differences

Path Handling: PowerShell vs Git Bash

PowerShell Path Handling:

# Native Windows paths work directly
$path = "C:\Users\John\Documents"
Test-Path $path  # True

# Forward slashes also work in PowerShell 7+
$path = "C:/Users/John/Documents"
Test-Path $path  # True

# Use Join-Path for cross-platform compatibility
$configPath = Join-Path -Path $PSScriptRoot -ChildPath "config.json"

# Use [System.IO.Path] for advanced scenarios
$fullPath = [System.IO.Path]::Combine($home, "documents", "file.txt")

Git Bash Path Handling:

# Git Bash uses Unix-style paths
path="/c/Users/John/Documents"
test -d "$path" && echo "Directory exists"

# Automatic path conversion (CAUTION)
# Git Bash converts Unix-style paths to Windows-style
# /c/Users → C:\Users (automatic)
# Arguments starting with / may be converted unexpectedly

# Use cygpath for manual conversion
cygpath -u "C:\path"      # → /c/path (Unix format)
cygpath -w "/c/path"      # → C:\path (Windows format)
cygpath -m "/c/path"      # → C:/path (Mixed format)

Automatic Path Conversion in Git Bash (CRITICAL)

Git Bash/MSYS2 automatically converts paths in certain scenarios, which can cause issues:

What Triggers Conversion

# Leading forward slash triggers conversion
command /foo         # Converts to C:\msys64\foo

# Path lists with colons
export PATH=/foo:/bar  # Converts to C:\msys64\foo;C:\msys64\bar

# Arguments after dashes
command --path=/foo    # Converts to --path=C:\msys64\foo

What's Exempt from Conversion

# Arguments with equals sign (variable assignments)
VAR=/foo command      # NOT converted

# Drive specifiers
command C:/path       # NOT converted

# Arguments with semicolons (already Windows format)
command "C:\foo;D:\bar"  # NOT converted

# Double slashes (Windows switches)
command //e //s       # NOT converted

Disabling Path Conversion

# Disable ALL conversion (Git Bash)
export MSYS_NO_PATHCONV=1
command /foo  # Stays as /foo

# Exclude specific patterns (MSYS2)
export MSYS2_ARG_CONV_EXCL="*"           # Exclude everything
export MSYS2_ARG_CONV_EXCL="--dir=;/test"  # Specific prefixes

When to Use PowerShell vs Git Bash on Windows

Use PowerShell When:

• ✅ Windows-specific tasks - Registry, WMI, Windows services
• ✅ Azure/Microsoft 365 automation - Az, Microsoft.Graph modules
• ✅ Module ecosystem - Leverage PSGallery modules
• ✅ Object-oriented pipelines - Rich object manipulation
• ✅ Native Windows integration - Built into Windows
• ✅ CI/CD with pwsh - GitHub Actions, Azure DevOps
• ✅ Cross-platform scripting - PowerShell 7 works on Linux/macOS

Example PowerShell Scenario:

# Azure VM management with Az module
Connect-AzAccount
Get-AzVM -ResourceGroupName "Production" |
    Where-Object {$_.PowerState -eq "VM running"} |
    Stop-AzVM -Force

Use Git Bash When:

• ✅ Unix tool compatibility - sed, awk, grep, find
• ✅ Git operations - Native Git command-line experience
• ✅ POSIX script execution - Running Linux shell scripts
• ✅ Cross-platform shell scripts - Bash scripts from Linux/macOS
• ✅ Text processing - Unix text utilities (sed, awk, cut)
• ✅ Development workflows - Node.js, Python, Ruby with Unix tools

Example Git Bash Scenario:

# Git workflow with Unix tools
git log --oneline | grep -i "feature" | awk '{print $1}' |
    xargs git show --stat

Shell-Aware Script Design

Detect and Adapt (PowerShell)

# Detect if running in PowerShell or Git Bash context
function Test-PowerShellContext {
    return ($null -ne $PSVersionTable)
}

# Adapt path handling based on context
function Get-CrossPlatformPath {
    param([string]$Path)

    if (Test-PowerShellContext) {
        # PowerShell: Use Join-Path
        return (Resolve-Path $Path -ErrorAction SilentlyContinue).Path
    }
    else {
        # Non-PowerShell context
        Write-Warning "Not running in PowerShell. Path operations may differ."
        return $Path
    }
}

Detect and Adapt (Bash)

# Detect shell environment
detect_shell() {
    if [ -n "$MSYSTEM" ]; then
        echo "git-bash"
    elif [ -n "$PSModulePath" ]; then
        echo "powershell"
    elif [ -n "$WSL_DISTRO_NAME" ]; then
        echo "wsl"
    else
        echo "unix"
    fi
}

# Adapt path handling
convert_path() {
    local path="$1"
    local shell_type=$(detect_shell)

    case "$shell_type" in
        git-bash)
            # Convert Windows path to Unix style
            echo "$path" | sed 's|\\|/|g' | sed 's|^\([A-Z]\):|/\L\1|'
            ;;
        *)
            echo "$path"
            ;;
    esac
}

# Usage
shell_type=$(detect_shell)
echo "Running in: $shell_type"

Environment Variable Comparison

Common Environment Variables

Cross-Shell Variable Access

PowerShell accessing environment variables:

$env:PATH              # Current PATH
$env:PSModulePath      # PowerShell module paths
$env:MSYSTEM           # Would be empty in PowerShell
[Environment]::GetEnvironmentVariable("PATH", "Machine")  # System PATH

Git Bash accessing environment variables:

echo $PATH             # Current PATH
echo $MSYSTEM          # Git Bash: MINGW64, MINGW32, or MSYS
echo $PSModulePath     # Would be empty in pure Bash

Practical Examples

Example 1: Cross-Shell File Finding

PowerShell:

# Find files modified in last 7 days
Get-ChildItem -Path "C:\Projects" -Recurse -File |
    Where-Object { $_.LastWriteTime -gt (Get-Date).AddDays(-7) } |
    Select-Object FullName, LastWriteTime

Git Bash:

# Same operation in Git Bash
find /c/Projects -type f -mtime -7 -exec ls -lh {} \;

Example 2: Process Management

PowerShell:

# Stop all Chrome processes
Get-Process chrome -ErrorAction SilentlyContinue | Stop-Process -Force

Git Bash:

# Same operation in Git Bash
ps aux | grep chrome | awk '{print $2}' | xargs kill -9 2>/dev/null

Example 3: Text File Processing

PowerShell:

# Extract unique email addresses from logs
Get-Content "logs.txt" |
    Select-String -Pattern '\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b' |
    ForEach-Object { $_.Matches.Value } |
    Sort-Object -Unique

Git Bash:

# Same operation in Git Bash
grep -oE '\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b' logs.txt |
    sort -u

Troubleshooting Cross-Shell Issues

Issue 1: Command Not Found

Problem: Command works in one shell but not another

# PowerShell
Get-Process  # Works

# Git Bash
Get-Process  # Command not found

Solution: Understand that PowerShell cmdlets don't exist in Bash. Use native commands or install PowerShell Core (pwsh) in Git Bash:

# Run PowerShell from Git Bash
pwsh -Command "Get-Process"

Issue 2: Path Format Mismatches

Problem: Paths don't work across shells

# Git Bash path
/c/Users/John/file.txt  # Works in Bash

# PowerShell
Test-Path "/c/Users/John/file.txt"  # May fail

Solution: Use cygpath for conversion or normalize paths:

# Convert to Windows format for PowerShell
win_path=$(cygpath -w "/c/Users/John/file.txt")
pwsh -Command "Test-Path '$win_path'"

Issue 3: Alias Conflicts

Problem: ls, cd, cat behave differently

# PowerShell
ls  # Actually runs Get-ChildItem

# Git Bash
ls  # Runs native Unix ls command

Solution: Use full cmdlet names in PowerShell scripts:

# Instead of: ls
Get-ChildItem  # Explicit cmdlet name

Best Practices Summary

PowerShell Scripts

1. ✅ Use $PSScriptRoot for script-relative paths
2. ✅ Use Join-Path or [IO.Path]::Combine() for paths
3. ✅ Avoid hardcoded backslashes
4. ✅ Use full cmdlet names (no aliases)
5. ✅ Test on all target platforms
6. ✅ Use $IsWindows, $IsLinux, $IsMacOS for platform detection

Git Bash Scripts

1. ✅ Check $MSYSTEM for Git Bash detection
2. ✅ Use cygpath for path conversion when needed
3. ✅ Set MSYS_NO_PATHCONV=1 to disable auto-conversion if needed
4. ✅ Quote paths with spaces
5. ✅ Use Unix-style paths (/c/...) within Bash
6. ✅ Convert to Windows paths when calling Windows tools

Cross-Shell Development

1. ✅ Document which shell your script requires
2. ✅ Add shell detection at script start
3. ✅ Provide clear error messages for wrong shell
4. ✅ Consider creating wrapper scripts for cross-shell compatibility
5. ✅ Test in both PowerShell and Git Bash if supporting both

Resources

• PowerShell Documentation
• Git for Windows Documentation
• MSYS2 Documentation
• Cygpath Documentation

Last Updated: October 2025